Initial implementation: AI code review bot for Gitea

- CLI binary with flag/env var configuration
- Gitea API client (PR metadata, diff, CI status, post review)
- OpenAI-compatible LLM client
- Structured review prompt with conventions support
- JSON response parser with validation
- Markdown review formatter for Gitea
- CI failure auto-detection (REQUEST_CHANGES)
- Dry-run mode for testing

gitea/client.go

@@ -0,0 +1,148 @@
+package gitea
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+)
+
+// Client interacts with the Gitea API.
+type Client struct {
+	BaseURL string
+	Token   string
+	HTTP    *http.Client
+}
+
+// NewClient creates a new Gitea API client.
+func NewClient(baseURL, token string) *Client {
+	return &Client{
+		BaseURL: strings.TrimRight(baseURL, "/"),
+		Token:   token,
+		HTTP:    &http.Client{},
+	}
+}
+
+// PullRequest holds relevant PR metadata.
+type PullRequest struct {
+	Title  string `json:"title"`
+	Body   string `json:"body"`
+	Head   struct {
+		Sha string `json:"sha"`
+	} `json:"head"`
+}
+
+// CommitStatus represents a single CI status entry.
+type CommitStatus struct {
+	Status      string `json:"status"`
+	Context     string `json:"context"`
+	Description string `json:"description"`
+	TargetURL   string `json:"target_url"`
+}
+
+// GetPullRequest fetches PR metadata.
+func (c *Client) GetPullRequest(owner, repo string, number int) (*PullRequest, error) {
+	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d", c.BaseURL, owner, repo, number)
+	body, err := c.doGet(url)
+	if err != nil {
+		return nil, fmt.Errorf("fetch PR: %w", err)
+	}
+	var pr PullRequest
+	if err := json.Unmarshal(body, &pr); err != nil {
+		return nil, fmt.Errorf("parse PR JSON: %w", err)
+	}
+	return &pr, nil
+}
+
+// GetPullRequestDiff fetches the unified diff for a PR.
+func (c *Client) GetPullRequestDiff(owner, repo string, number int) (string, error) {
+	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d.diff", c.BaseURL, owner, repo, number)
+	body, err := c.doGet(url)
+	if err != nil {
+		return "", fmt.Errorf("fetch diff: %w", err)
+	}
+	return string(body), nil
+}
+
+// GetCommitStatuses fetches CI statuses for a commit SHA.
+func (c *Client) GetCommitStatuses(owner, repo, sha string) ([]CommitStatus, error) {
+	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/commits/%s/statuses", c.BaseURL, owner, repo, sha)
+	body, err := c.doGet(url)
+	if err != nil {
+		return nil, fmt.Errorf("fetch commit statuses: %w", err)
+	}
+	var statuses []CommitStatus
+	if err := json.Unmarshal(body, &statuses); err != nil {
+		return nil, fmt.Errorf("parse statuses JSON: %w", err)
+	}
+	return statuses, nil
+}
+
+// GetFileContent fetches a file from the default branch of a repo.
+func (c *Client) GetFileContent(owner, repo, filepath string) (string, error) {
+	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/raw/%s", c.BaseURL, owner, repo, filepath)
+	body, err := c.doGet(url)
+	if err != nil {
+		return "", fmt.Errorf("fetch file %s: %w", filepath, err)
+	}
+	return string(body), nil
+}
+
+// PostReview submits a review to a PR.
+// event should be "APPROVED" or "REQUEST_CHANGES".
+func (c *Client) PostReview(owner, repo string, number int, event, body string) error {
+	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d/reviews", c.BaseURL, owner, repo, number)
+
+	payload := struct {
+		Body  string `json:"body"`
+		Event string `json:"event"`
+	}{
+		Body:  body,
+		Event: event,
+	}
+
+	data, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshal review payload: %w", err)
+	}
+
+	req, err := http.NewRequest("POST", url, strings.NewReader(string(data)))
+	if err != nil {
+		return fmt.Errorf("create review request: %w", err)
+	}
+	req.Header.Set("Authorization", "token "+c.Token)
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.HTTP.Do(req)
+	if err != nil {
+		return fmt.Errorf("post review: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		respBody, _ := io.ReadAll(resp.Body)
+		return fmt.Errorf("post review failed (status %d): %s", resp.StatusCode, string(respBody))
+	}
+	return nil
+}
+
+func (c *Client) doGet(url string) ([]byte, error) {
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Authorization", "token "+c.Token)
+
+	resp, err := c.HTTP.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("HTTP %d: %s", resp.StatusCode, string(body))
+	}
+	return io.ReadAll(resp.Body)
+}